Cellular collapse can turn brown with time...
I see that you have posted a thread on slippertalk, some experts can help you because i'm not a plant pathologist. I will link this thread there since you didn't load the pictures on ST.
Virus? - Slippertalk.com - Slipper Orchid Forum for Paphs, Phrags other slipper orchids
I am sure that it is not a virus, but you can get it tested if you wish.
It may just be a rot, that is curable. Maybe a fungal one
Worst case scenario would be Erwinia, but I am not certain.
I think using physan 20 wouldn't hurt